1. Field of the Invention
The present invention relates generally to improvements in cameras and it relates particularly to an improved motor focussed, single-lens reflex camera of the interchangeable objective lens type.
In the conventional objective lens exchangeable single-lens reflex cameras, focussing of the objective lens is performed by rotating a focussing ring provided on the objective lens barrel. However, when an automatic focussing device is incorporated in the single-lens reflex camera and a drive device such as an electric motor controlled by the automatic focussing device is used to rotate the focussing ring for focussing an objective lens, it is almost impossible to control the focus of all types of objective lenses, since the distance between the focussing and the camera body varies with the type of objective lens, as does the force required for rotating the focussing ring. Even if, in such type of camera, it is possible to automatically control the focus of all types of objective lenses a complex interlocking mechanism must be provided, thereby posing the problem of an appreciable increase in the size and price of the camera. In an attempt to solve this problem, there has been proposed a device in which an entire objective lens is longitudinally moved along the camera optical axis for controlling focus (U.S. Pat. No. 3,798,660 granted Mar. 19, 1979). With such device, however, the lens mounting member of the camera to which the exchangeable objective lens is mounted, is supported by a ring rotated by a motor within the camera and the rotatable ring itself serves as a guide member therefor, or the lens mounting member is restricted to movement along the optical axis by a guide pin fixed to the camera body. As a result, the length of the available lens shift is greatly limited, posing a further problem. Increasing the length of the available lens shift in such a device requires that the length of a rotatable ring supporting the lens mounting member be increased along the optical axis or that the guide pin be lengthened. However, such increase in size results in a larger camera body, causing much inconvenience. Consequently, the devices heretofore proposed possess the drawback that the length of available lens shift cannot be increased without an increase in the camera size.
Furthermore, with the earlier structures, a lens mounting member on which an exchangeable objective lens is mounted is formed as a cylindrical member, part of which is positioned near the viewer penta prism. In addition, the lens mounting member and its support must be thick and sturdy enough to withstand the weight of an exchangeable objective lens which is coupled to the lens mounting member, thereby necessitating the provision of a large space near the penta prism. Therefore, the earlier structures have the lens mounting member and the supporting member therefore assembled near the camera viewer penta prism, the design freedom of which is greatly impeded in terms of the penta prism arrangement.